Rasmussen’s numbers are usually a bit worse for democrats, not because they are wrong, but because they use a strict formula to calculate likely voters, not just registered voters.

Rasmussen’s polls are based on who is actually likely to turn out to vote, not on the general public mood. Rasmussen explains this on their website.
Republicans, churchgoers, conservatives, married people and seniors are more likely to voter than liberals, democrats and single youth. Its a fact.